Humanists, affirming that humanity is a “part of nature,” have urged responsible action on such problems as overpopulation and global warming since humanist organizations were created in the middle of the twentieth century. Many leading environmentalists, including Worldwatch founder Lester Brown, biologist E. O. Wilson, and animal rights advocate Peter Singer, have been publicly associated with the humanist movement. Yet some environmentalists, including Singer himself, fault humanism for deifying humanity and ignoring the dignity of other species. In the face of this criticism, some humanists seek to distance humanism from humanocentrism, while others insist that an optimistic confidence in human potential is preferable to ecological pessimism.